This invention relates to a process for the production of alcohol by continuous fermentation of a must in fermenters arranged in a cascade, in which fresh must and oxygen are continuously introduced at the beginning of the cascade and fermented must is continuously collected at the end of the cascade, and to an apparatus for the continuous production of alcohol comprising several fermenters arranged in a cascade.
There are various known processes and apparatus for the production of alcohol by fermentation of a culture medium rich in fermentable sugar which is referred to hereinafter as "must". Among the known processes, there are three main types which are discussed briefly hereinafter, namely, the batch process carried out in a single vat, the continuous process carried out in vats arranged in a cascade and the continuous process carried out in a circulation fermenter.
The batch process carried out in a single vat is still used today by virtue of its simplicity. Its principal disadvantage is its low productivity.
The continuous process carried out in vats arranged in a cascade, in which fresh must and oxygen are continuously introduced at the beginning of the cascade, in which the yeast circulates with the must from one vat to the other after having been produced or introduced into the first vat and in which fermented must is continuously collected at the end of the cascade, is no higher in its productivity than the single-vat batch process, but does avoid the interruptions in production and the need to clean the vat between two production batches.
The continuous process carried out in a circulation fermenter is distinguished by its high productivity due to the fact that it enables a high concentration of yeast, particularly flocculating yeast, to be used in the must. In this type of known process, the concentration of yeast in the must is kept at the desired value by recycling at least part of the yeast separated from the fermented must withdrawn. Now, the consequence of such recycling is a prolonged average residence time of the yeast in the fermenter.